I like your choices. I think Abbott is a cool name. I wouldn't worry to much about HAC. It's not like it's RAT or ZIT or HIV; and chances are she won't keep the C forever. ZAC is a little corny but Zac might think it's awesome. I know a guy who goes by Ash and his innitials are ASH and he thinks it's really cool. If Ben feels left out because everyone else has an E name, remind him that Etta is actually Henrietta, so techically it's an H. Or you could (jokingly) offer to call him Enjamin.